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This database was created and is curated by Barbara Flueckiger, professor at the Institute of Cinema Studies, University of Zurich. Please see more information about the project here. Support the further development of Timeline of Historical Film Colors via Stripe.

In 2013 the University of Zurich and Swiss National Science Foundation awarded additional funding for the elaboration of this web resource. 80 financial contributors sponsored the crowdfunding campaign Database of Historical Film Colors with more than USD 11.100 in 2012. In addition, the Institute for the Performing Arts and Film, Zurich University of the Arts provided a major contribution to the development of the database. Many further persons and institutions have supported the project, see acknowledgements.

Follow the links “Show detailed information →” to access the currently available detail pages for individual processes. These pages contain an image gallery, a short description, a bibliography of original papers and secondary sources connected to extended quotes from these sources, downloads of seminal papers and links. We are updating these detail pages on a regular basis.

Timeline of Historical Film Colors

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Principle

Invented by

Description

Dufaycolor was a regular mosaic screen process whereby the incident light was filtered through a pattern of tiny color patches in red, green and blue, the so called réseau. When viewed from an appropriate distance, the pattern fused in the eye of the observer to form a variety of hues – similar to the dots in Pointillism paintings. The Frenchman Louis Dufay invented this pattern for still photography (see Dioptichrome) in 1908. Different companies exploited the process and changed the arrangement several times during its evolution, but the principle remained the same.

The application of the réseau onto the film was a very complicated and demanding process. The acetate film base was first coated with a blue layer (see images on this page). Then a greasy ink resist was printed in diagonal lines at an angle of 23°. The remaining lines were bleached and subsequently dyed green. Afterwards the first resist was removed and a new layer of resist lines was applied at an angle of 90° to the first two lines. The remaining lines were bleached again and subsequently dyed red. As a result of this process a pattern was formed that consisted of blue and green rectangles in combination with thinner red lines so that all patches covered areas identical in size. Finally a varnish was applied to protect the réseau and the base was coated with a panchromatic emulsion. Exposure was done through the réseau on the black-and-white emulsion and the film developed by a b/w process, a majority by a reversal process. In the different systems the order of the colors varied. For instance the Spicer-Dufay stock consisted of the red and green rectangles with blue lines.

Although the pattern was very, very fine with 19 to 25 lines per millimeter thus resulting in a million and a half patches per square inch – which equals almost 1K in resolution – it was still visible on the screen due to the high degree of magnification in projection. However, while irregular screen processes failed completely as a result of the random pattern which emerged when the film was projected, the regular screen of the Dufaycolor process was far better adapted to moving pictures. More importantly, shooting, development and screening could be operated with the usual equipment for b/w cinematography. Therefore the process was a viable and cheap alternative to Technicolor. Documentaries, experimental films and home movies were shot in Dufaycolor (see list of films on this page).

Since up to 80% of light was absorbed by the filters, all the additive screen processes required high amount of light, both for exposure and projection. To compensate for the light absorption, the Dufaycolor dyes had flat overlapping spectral transmission curves (see image on this page) which led to the desaturation of the colors. Thus the hues appear muted.

Printing from negatives posed specific problems because interferences occur when two regular patterns are overlaid on top of each other, producing an artifact called moiré. Theoretically there were two solutions to this problem. Either the negative and the print should be aligned perfectly or the pattern of the negative had to be destroyed in the printing process. Since the first solution was impossible due to the very small tolerances necessary, the second solution was applied with an aperture mask in combination with diffuse light. Similar problems arise when Dufaycolor film has to be digitized, since the diagonal pattern of the film and the orthogonal pixel structure interfere equally. Therefore scanning requires very high resolution and a light source with three narrow bands for spectral transmission in the primaries, similar to the ones used in the Dufaycolor printing process (see image on this page).

A Colour Box (GB 1935, Len Lye) is an abstract animation for a commercial by the British post GPO. Len Lye’s hand-painted film was then transferred to a Dufaycolor print. See further information on Screen Online.

A Colour Box (GB 1935, Len Lye)

A Colour Box (GB 1935, Len Lye)

YouTube video in very low resolution shows the restoration of A Colour Box. An Eastmancolor print wastaken from the hand painted original nitrate as described by Anne Fleming (2002), see field “Restoration” on this page.

“INTEREST. Norman Hartnell fashions being produced and on show, featuring Lady Bridgett Poulett, Miss Peggy Hamilton and Miss Biddy Weir. Note 1: The relation between this film and DESIGN FOR SPRING (1937) is uncertain – the one may simply be a shorter version of the other, or MAKING FASHION is a new film in its own right, possibly produced from the same source material, or (most likely) they are the same film with a change of title. The credits are virtually identical. Here Dufay-Chromex are not credited on screen but are given as producers in the Kinematograph Year Book for 1939. The film was registered May 1938 as MAKING FASHIONS. DESIGN FOR SPRING, however, was reviewed in February 1938. Note 2: Dufay-Chromex records suggest that DESIGN FOR SPRING was withdrawn after exhibitors claimed that it was an advertising film, and subsequently re-issued 400ft shorter as MAKING FASHION. NFTVA copies of the two films are of identical length. (Shotlist)” (Synopsis BFI catalogue)

“Titles and credits (0.08) Scenes from George V’s Silver Jubilee procession, with crowds lining the streets. Buckingham Palace in background with crowd in foreground behind guardsmen. Band marches l-r. Open carriage comes through gates, towards camera then crosses l-r followed by horse guards. (0.28) CU of closed carriage with heavy ornamentation l-r (0.44) Followed by another open carriage. (0.54) Camera view from high up, looking down on street with white buildings in background. Pans l-r along buildings. (0.59) Procession comes towards camera down street (1.06) Procession r-l in front of Buckingham Palace (?). (1.11) CU open carriage r-l with King George V and Queen Mary in it. Camera pans left, following the carriage.(1.40) Guards, band on horseback and tartan guard march l-r (1.57) Race track, horses at far end gallop towards camera. (1.58) Men altering a display board. At top board says Windsor Castle Stakes. (2.00) Stalls (2.02) Well dressed men (in top hats) and women come through a gate. (2.07) Bi-plane (2 engines, with large white Y on it’s side in front of the wing, and a red dot behind) flies r-l, ascending. (2.17) Three RAF planes fly r-l ascending. (2.25) Signal flags flying in the fore ground, largely obscuring a boat in the background. (2.31) Two large ships filmed from stern. One in mid ground has one funnel (red below, black top). One in back ground has two funnels. Both have bunting from masts. Small boat in foreground. (2.39) (Shotlist)” (BFI catalogue)

Limbacher (1969): Four Aspects of the Film. A History of the Development of Color, Sound, 3-D and Widescreen Films and Their Contribution to the Art of the Motion Picture. New York: Brussel & Brussel 1969, 386 pp. 44-45. View Quote

Limbacher (1969): Four Aspects of the Film. A History of the Development of Color, Sound, 3-D and Widescreen Films and Their Contribution to the Art of the Motion Picture. New York: Brussel & Brussel 1969, 386 pp. 44-45:

A color sequence in a film called THE RADIO PARADE (CAN 1934, Norman McLaren)

“THE ENGLISH DUFAYCOLOR FILM PROCESS [Presented at the Spring, 1934, Meeting at Atlantic City, N. J.]

W. H. CARSON [New York, N. Y.]

Summary. The Dufaycolor three-color additive system of color cinematography, employing a geometrical color-screen or réseau imprinted on the film base, is briefly described. As many as a million color elements per square inch are employed, and a correct color balance is achieved by adjusting the area covered by the blue dye in relation to that covered by the two other primary colors. No appreciable changes of equipment are required in applying the system commercially, either in photographing, processing, or projecting, from what is now found in use.

Many may wonder at the presentation of a paper on a subject as old in color photography as a color-screen process. However, the developments of the past two years have proved the process to be no longer in the theoretical and experimental stages but on a practical and commercial basis, and for that reason a discussion of the new Dufaycolor system seems to be in order.

Any engineering group may rightly be skeptical of the recommendation or adoption of any innovation in the industry that can not conclusively demonstrate its basic soundness in both the theoretical and practical fields. However, past experience has shown that new scientific developments and improvements must be injected into the industry from the bottom up rather than from the top down.

The introduction of sound into the motion picture industry came after years of research and the expenditure of millions of dollars in experimentation, which have been little recognized by the layman or the box-office patron. It was only through the tremendous pressure brought to bear by the sound technicians who visualized its future that it was finally grudgingly accepted by the producer and exhibitor and even more reluctantly by the public. Today it is impossible for silent productions to compete with talking pictures.

The whole technic of producing silent motion pictures, including script writing, directing, acting, photographing, lighting, stage construction, processing, projection, and theater construction, has been revolutionized to serve the new medium of sound. But in return for all that, a broadened scope of dramatic and popular application of sound pictures with respect to their increased entertainment value has been found. Since we are dealing with an industry that depends for its continued prosperity on its dollar-and-cent value and an adequate return to its stock-holders, it must be admitted that the advent of sound motion pictures has enabled the motion picture industry to retain a position in the entertainment field through a most trying period, when almost every other industry in the luxury field has been forced into bankruptcy, if not completely annihilated.

Color in motion picture photography must enjoy the same consideration in planning productions, selecting subjects, actors, make-up, costumes, settings, in directing, lighting, and photographing, that is now being given to sound, if it is to contribute as fully to the progress of the industry; but it can not fail to assume a position of similar importance in the very near future. No claim for originality is made for these statements, and recognition must fairly be given to the pioneer work that has been done by Technicolor under the able direction of Dr. Herbert T. Kalmus along those lines. The progress that has been made up to the present in recognizing a distinct technic in color production lends some encouragement to the conviction that producers are awake to the possibilities of color, and are only waiting to be shown the practical means of application and be assured consistently satisfactory results on duplication before making it a major consideration in future productions.

The first question that arises is whether colored motion pictures having a true color fidelity throughout the full range of the visible spectrum can be produced commercially for a slightly increased cost, which increase might be justified by an increase either in the box-office receipts or in entertainment value, permitting the motion picture to maintain or improve its present outstanding value as entertainment so that financially it may continue to compete successfully against other and newer amusements.

No industry that occupies such a paramount position as the motion picture industry occupies in the amusement field can afford to “rest on its oars” during a time when changing conditions in the social order are creating a superabundance of leisure for the average person, who can now indulge more frequently in the pleasures that formerly he was able to enjoy only to a limited extent; or, if these are not sufficient to satisfy his need, seek new and other diversions with which to fill his time. Countless thousands of dollars are being spent to create, on an ever-increasing scale, extravagant and spectacular productions that must in time break down of their own weight.

Some new and startling feature must be introduced to rejuvenate the appeal, a feature that would admit of simplifying or abandoning the costly artificial settings and bring into play a new artistic medium, which, while new in motion pictures, is one of the primal appeals to which human beings react color.

After a comprehensive study of all the theoretical processes available and those that have been in a measure successful, the conclusion was reached that two-color and three-color optical and imbibition processes have not, with existing equipment, both taking and projection, given a result on the theatrical screen that will satisfactorily fulfill these various requirements. The ideal method of producing colored motion pictures would seem to be a system by which such colored pictures could be made with the existing cameras and lighting equipment, and supplied to the exhibitor for satisfactory use on his present projection equipment without expensive alterations; and, what is equally as important, to accomplish that result without any radical change in the present laboratory procedure. Thus it would be possible for every producing company to add color as a supplementary feature to its productions without disrupting its organization or making large capital investments. All these requirements are fulfilled by the Dufaycolor process, here described.

For ordinary transparency purposes little importance seems to be attached to the pattern of the screen so long as the three primary additive color elements are present in the proper balance and proportion.

Dufaycolor, Lumière, Agfa, Finlay, or other transparencies that are really representative of these systems will all produce apparently perfect color rendition with suitable transmitted light if viewed at a distance of about eighteen inches by the average eye or projected from standard lantern-slide size to the usual small-screen size.

Where non-geometrical color-screens are used it necessarily happens that masses of the red, blue, or green units occur in the form of blotches or larger areas, and it is obvious that for achieving perfect effects on greater magnification better results can be attained when the three primary color elements are regularly broken up into the smallest possible units and uniformly distributed. For that reason the geometric matrix or réseau, as it is termed, seems to have a decided advantage. It is believed that the Dufay system is the first screen process in which projection from standard 35-mm. film to theatrical screen size has been seriously attempted. The application of a réseau of this kind to a film base by mechanical means, on a regular and comparatively inexpensive commercial basis, further seems to enhance its value as an acceptable medium for use in the professional motion picture field.

The idea of applying a series of colored lines or squares to the film base, originally suggested by Vidal in 1895, was used by Dufay in the further development of the process under discussion, wherein a contiguous series of red and green squares (or any two of the primary colors) were placed alternately between lines of blue (or the third primary color). Theoretically it would not seem to be of great importance as to what order was used in the application of the three primary colors. In practice it was found that on account of the high visual contrast of the blue line, the screen so constructed was much more visible when magnified to the extent necessary in motion picture work than a different arrangement. At present the screen is produced with blue and red squares and a green line, which has the effect of reducing the visibility of the screen on projection.

It is obvious that the smaller the area of each individual unit, the more perfect will be the blending of the color units by the eye, even upon excessive enlargement, and the less the effect on image definition. It was formerly believed that fifteen lines to the millimeter was the limit of practical mechanical production, but within the last year a screen having nineteen lines to the millimeter (i. e., one thousand lines and spaces to the inch) has been very satisfactorily produced, and recent improvements point to a still further reduction of the line width. Even with the present line width it has been found that the réseau is not visible beyond the first six rows of the seats in the average theater. This provides the present screen with approximately a million color elements to the square inch, and further diminution will have a progressively startling effect in definition and luminosity.

The statement that such a screen or réseau can be produced mechanically, consistently, in large quantities, on a commercial basis, and at a reasonable cost, will bear some scrutiny; so the first question that arises is, has it been done? The answer is that it is now being done by a reputable and well-known English manufacturer on 21-inch acetate motion picture base in 1000-foot lengths at the rate of 90,000 35-mm. ciné feet per week. Increased production is contemplated immediately, and the reception of the film by the English producers has been very enthusiastic.

The next question is, how is it done? A film base of suitable thickness (acetate base has been used exclusively because eventually legal restrictions will require it, but similar results are possible on nitrate) is first coated with a thin layer of collodion containing a dye, let us say blue, adjusted to the spectral hue of the blue primary.

After drying, the film is then passed through a highly specialized type of rotary printing machine consisting of a steel roller milled one thousand lines to the inch (really five hundred lines, with an equal number of spaces between). The machine embodies an elaborate ink distribution device for the roller; and underneath, in contact with it, a soft rubber covered roller capable of minute vernier concentric adjustment for controlling pressure. The ink used on the press is a special kind, forming a moisture resistant line printed upon the basic color. The idea of using a greasy resist was first suggested by du Hauron and Bercegol in 1907. And here again reference should be made to the remarkable far-sightedness of Louis Dufay in the application of the basic principle of the geometric screen and the use of resistant medium for applying the primary colors to the film base by mechanical means.

In the development of any new idea, there must be some individual or group that has enough faith in its ultimate value to be willing to finance it through the sterile years when salaries must be paid and valuable council and encouragement given in the face of apparently meager progress. It has been fortunate that this process has been sponsored by Spicers, Ltd., of London. This firm, manufacturers of all kinds of fine paper products, is an old English family organization, whose commercial solidity has enabled them to keep their wheels turning through the past lean years, and who have provided the financial backing and the technical guidance of such men of their organization as A. Dykes Spicer and S. R. Wycherley to bring this process to its present degree of perfection. However, the credit for the practical application of the resist on a commercial scale must be given to Charles Bonamico, a French engineer with Spicer-Dufay. His engineering skill in perfecting a means of milling a steel roller for applying the lines, and the subsequent control of application of the ink, marks one of the outstanding factors in the success of the process.

Although the ink used in applying the resist is much thinner than would ordinarily be used for typographic purposes, under suitable conditions it assumes a partially dry state, providing lines having substantially sharp parallel edges and free from blur or creep, and when subsequently passed through a properly selected bleaching bath, produces perfectly clear white lines between the ink-protected lines.

In the same machine, which has been especially designed for the process, the film is then passed into a bath containing dye of such concentration that will give the primary red on the intermediate bleached white lines. Allowing time and space for suitable washing to remove the excess red dye, the film then passes into a solution and a mechanical scrubbing action removes the protective ink. A simple diagram illustrating the method is shown in Fig. 1. If at this stage the film be examined with a microscope, we shall find that it is covered with a fine grid of alternating blue and red lines, having the same width and with perfectly contiguous but not overlapping edges, and each line representing a perfect primary filter in the two colors named (Fig. 2).

After drying, the film is again passed through a similar rotary printing machine, but this time the lines on the printing rollers are at an angle of about forty-five degrees to the original lines (theoretically the best angle is not forty-five degrees: this has a very important bearing on other features of the process). The width of the lines applied in this operation is not the same as that of the lines applied in first, but is so controlled that the imprinted area alongside two contiguous squares, so formed, is equal to the area of each of the squares. The film is then bleached in a manner similar to that formerly described, the bleached line is dyed the third primary color (green), and the resisting ink is then removed in the same manner as described before (refer to Fig. 1). The film is then dried and wound up. This arrangement produces a perfectly balanced neutral grey screen when viewed or projected. When examined microscopically, a réseau such as illustrated in Fig. 3 is seen.

The next question refers to the emulsion to be applied to this réseau. While there are, of course, many applications for color film and the emulsion characteristics are correspondingly numerous, for the present only those that apply to cinematography will be considered.

It is interesting to note that in the very early stages of color development the theorists visualized an emulsion that was truly panchromatic and had a high speed and very fine grains. As no such emulsion existed at that time they approached the emulsion makers much as Macbeth sought the witches of Endor and suggested some diabolical brews that too often resulted in nothing more than toil and trouble, and never achieved results on a practical basis.

For that reason it may be said that the development of color photography has had to mark time until the art of emulsion making could catch up with its theoretical requirements, and it is believed that that time has now arrived.

It would be of interest to review some of the problems of the photographic chemists. The art of emulsion making formerly depended upon controlling the balance of silver halide and gelatin characteristics, together with delicate manipulation of heating, digestion, washing, ripening, etc., with more or less crude equipment.

Today those factors have been so well correlated as to establish a science; and emulsion making equipment has become practically standardized, with automatic engineering controls that assure an accuracy permitting duplication of results within remarkably narrow limits.

Considering also the great strides that have been made within the past few years by all the large photographic manufacturers, both in this country and abroad, in controlling the size of grain of super-speed emulsions without increasing the fog or impairing the keeping quality; and further, in developing new sensitizers by means of which emulsions can be made selective to any portion of the spectrum, visible, infra-visible, and supra-visible, it can be understood that problems in the reproduction of color, that seemed insurmountable a few years ago, have now been resolved by the progress that has been made in the black-and-white field of the art. The application of these advances to color photography now realizes satisfactory results where before the same efforts met only with failure.

So now, for the requirements of this process, emulsions may be selected practically according to specification, provided the basic, characteristics of the process are known. These factors are all well known, and are the same as those now operating in black-and-white technic: they may be briefly mentioned as speed, color-sensitivity, grain size, gradation, and gamma. With slight modification it may be said that a good panchromatic emulsion, rich in silver as compared with its gelatin content, with a color-sensitivity that will produce, as nearly as possible, the same density with all three of the primary colors, with a fine grain, and high speed will serve admirably for the process. Such an emulsion is now being used.

There are several important characteristics that had to be considered in selecting the emulsion that might be well discussed at greater length. First, the effect of wavelength on the gradation and gamma: Experience has shown that the effect of wavelength on gamma is negligible, provided it is measured at gamma infinity; but that, of course, must be considered in relation to exposure, development, and intermediate gradation. For that reason an emulsion has been selected that has a long straight line in its characteristic curve together with a short toe. So much progress has been made within the past few months that it is impossible to show by graphs the curves of the emulsion now being used, but it may be said that the range of latitude in the present emulsion is far greater than it was thought possible to produce a year ago. In any screen process it is imperative that the emulsion, no matter how thinly it may be coated, be capable of giving intense blacks, so that any colored area on the réseau may be effectually blocked out, allowing no dilution of the true color by the transmission of a foreign color that is not truly an additive component of the colors in the object being photographed.

Second is the question of the spectral value of the filters. Various statements have been made as to the proportion of the incident light that passes through the many types of matrices used in the various processes, and have ranged from ten to twenty-five per cent. In the Dufaycolor process the filter colors selected do not transmit in short narrow bands, but rather overlap from one to another much in the manner shown in Fig. 4.

Whether that is theoretically the proper way to produce true color in a three-color additive process is of no particular concern if a result having a satisfactory color fidelity for the average eye is achieved. At the same time, such a procedure results in marked advantage as to the proportion of light transmitted to the emulsion on the taking film, and increases the luminosity of the resultant picture on the screen with ordinary projection light. (It has been noticed in this connection that a lower screen luminosity seems to be acceptable in color pictures than would be regarded as satisfactory in black-and-white.) The use of filters having such overlapping transmission characteristics may raise a question concerning the dilution of color on reproduction, but that will be covered later. The filters used also provide a remarkable increase in the latitude of exposure and development as compared with matrices in which filters having narrow transmission bands are used.

Much advancement has been made in England in the past two years in perfecting dyes capable of very much greater light transmission than was formerly attained, without sacrificing their spectral fidelity. These new dyes have been adopted by Dufaycolor. A method has been found to isolate them from the emulsion so that no desensitizing action takes place, and excellent adhesion between the matrix and the emulsion, which has heretofore often been unsatisfactory and extremely difficult to attain, has been accomplished.

The two factors of increased speed of modern panchromatic emulsions and better dyes for the filters have made possible a film having a speed hitherto unattainable in screen processes.

Any color process that does not provide for duplication in unlimited quantities, of consistent fidelity, and on a commercial scale is, of course, not worthy of consideration. It is believed that methods have been found and patented by which to accomplish such results to such a high degree of satisfaction that it is almost impossible to distinguish between originals made in the camera for projection and copies made from the original master positive. Up to last year it was believed that the same type of emulsion would serve both for taking and for making subsequent copies or dupes. At present, however, it is believed that the master positive, which might be called the original (and made in the camera), should have a heavy coating of emulsion as compared with the stock used for copies.

When it is reversed it seems quite flat and the colors feeble, but when duplicates are made from it by the latest methods on a suitable printing stock, the colors come up to full strength. The maximum density is about 1.2, and a very wide range of gradation is maintained.

It has not been found possible to produce an emulsion adapted to all light conditions, natural (daylight) and artificial (arc and incandescent), without using a compensating filter of some sort. Because of the fact that a large proportion of professional motion picture photography is done under artificial light it seems best for the moment to adapt the film to artificial lighting, and to compensate for other conditions by using the proper filters. While very fast emulsions have been developed for the system, no claim is made that the speed is comparable with that of black-and-white, since there must be a marked reduction in the transmission in any color process.

However, a speed has been attained that makes it possible to fulfill the requirements of motion picture studios with the existing lenses and lighting equipment.

Now regarding laboratory treatment: Many studios are at present working on the “master positive” basis, on which a positive is made by reversal from the edited first print after the cutting and timing have been done in order to gain the advantage of reduced graininess and uniformity of density. Although no reference has been previously made, it is understood, of course, that the original film under this process is reversed to produce a positive result (it is possible to develop the film as a negative and make positive prints therefrom).

The procedure in reversal is standard. Developers of various kinds have been tested, the best results having been achieved with M-Q ammonia of rather high concentration at 65° F. After the bleaching and the second exposure, the second development occurs in an ordinary metol-hydroquinone developer, and it is recommended that the second development be carried on under full illumination. It may be well to mention that by reversal the usual advantage of eliminating the larger grains of the emulsion is gained, leaving the smaller grains to form the reversed image. It should be noted also that the entire procedure can be accomplished on existing motion picture developing machines with only very slight, if any, modification, and is therefore adaptable without expensive changes in equipment or personnel by any producing company that operates its own laboratory.

No mention has as yet been made regarding the possibility of recording sound on the film; but that, of course, has been given full consideration. Several methods have been devised and patented for removing the screen or réseau, before the film is coated with emulsion, from the space along the edge of the film to be occupied by the sound track. In practice it has been found that such a procedure is not necessary, as the number of lines in the screen that is used is so great that any effect it may produce on the various types of sound recording equipment now in use will not produce a reaction within the audible range. Recording can be done by either the variable width or the variable density method if the intensity of the recording light source is increased enough to offset the reduction of light transmission by the réseau. Similar remarks apply to the reproduction of sound during projection.

The emulsion, which has been described as ideal for color reproduction, is of the same type that would be selected by the sound engineer as the best for true sound reproduction. Sound has been recorded on all the standard systems, including the Movietone News camera, wherein a sound record was taken, through the réseau, on the same film as that used for the picture. Originals and copies have given excellent sound reproduction and, although several English sound experts have expressed the belief that the réseau would interfere with some of the higher frequencies of the audible range, as yet no such interference has been detected in practice.

It has long been thought that it was impossible to reproduce from a screen transparency having a geometrical design due to the difficulty of exactly registering the colored areas in the original with the similar colored areas in the copy. The problem of avoiding moiré effects in reproducing through a geometrical screen has also been adjudged insurmountable but several simple and very ingenious methods have been developed to circumvent both those problems.

Most of the research in the development of this process, theoretical and scientific, has been done by T. Thorne Baker, a member of our Society. Many of the statements in this paper are based upon data that he has supplied.

Many technical points have been brought out in this paper that have not been fully covered; but as the purpose of this presentation is simply to describe the general process, it is hoped that further opportunity will be given later for their more detailed discussion.

DISCUSSION

MR. MITCHELL: What is the relative speed, compared to black-and-white?

MR. CARSON: Developments are occurring so rapidly that I hesitate to answer. I will say, however, that the film that I am showing here is approximately one-fourth as fast as black-and-white. We made some that were only one third as fast. The fastest emulsion receives through the screen about one-third the light incident on the film.

MR. PALMER: Is the picture you are to show a reversal print or a print from the original?

MR. CARSON: Both. The first is an original or master positive, as made in the camera. The second will be a print made from some of the same scenes as a duplicate, made in England. It was developed under rather unfavorable conditions by rack and tank, and not by machine; and the evidences of the rack marks are present in the print.

MR. POPOVICI: What kind of light was used for photographing? Arc or incandescent?

MR. CARSON: Arc and incandescent, I understand. I did not see the exposures made, as they were made in England.

DR. GOLDSMITH: Approximately how many lines are there across the screen?

MR. CARSON: Nineteen lines to the millimeter, or approximately one million elements to the square inch. With 25 lines to the millimeter, which is the screen that will be produced next, there will be approximately a million and a half to the square inch. The luminosity and the definition will both increase. The light we are using here is the standard light for black-and-white pictures. Even though there is stray light on the screen, which would not occur under good conditions, the picture is sufficiently bright. That is a fact that I mentioned in the paper that a lower screen brilliancy seems to be acceptable with color than with black-and-white.

MR. BATSEL: Are the prints made by contact or by projection?

MR. CARSON: Projection. We are not ready to discuss the method of printing right now, for patent reasons; but I will say that it was the combined work of the Ilford group, under the direction of Dr. Renwick, who was formerly with the Dupont Company. The film was made by the Ilford, Limited.

MR. SACHTLEBEN: What difficulties, if any, are experienced in obtaining proper registration of the colors when making a print? How do you manage to have the greens green and the blues blue and not something else?

MR. CARSON: A means has been devised of interposing a prism type of lens between the two films on the projection printer, which divides into four each of the color areas in the original screen as it prints, so that any color area is bound to fall on one similar to it.

MR. CRABTREE: Was the original developed by machine or by rack-and-tank?

MR. CARSON: By rack, also.

MR. KELLOGG: One would expect, with the extent of the overlap of the spectral regions, that the printing process you just described would cost something in saturation.

MR. CARSON: Theoretically, each time you step down, a certain dilution occurs due. to the overlaps. Here, again, means were found of eliminating the overlap in the printing operation. While there is some dilution, there is not very much. With proper laboratory treatment and machine control, duplicates can be produced that are entirely satisfactory for commercial use.

MR. SACHTLEBEN: Mr. Carson stated that the quality of the print was superior to that of the original. I believe that has been quite well borne out in this demonstration.

MR. CARSON: We don’t consider it so. You misunderstood me.

MR. SACHTLEBEN: I found the second reel that was shown more pleasing than the first.

MR. CARSON: The fact of whether it is more pleasing to the eye or not is something that is more or less a matter of personal taste. What I meant to say was the spectral fidelity of the original is greater than the spectral fidelity of the duplicates.

I do not believe that the duplicates are exactly as good as the original.

If you saw the two run side by side, you could distinguish the difference. If you saw one run in one place and one in another, they would appear so nearly alike that you would find it difficult to say which was which.”

“Since the 1890s there had been a number of still colour photographic processes in which a regular or irregular fine mosaic of microscopic colour filters was produced on the surface of a glass plate or film. Coated with emulsion, the plate or film was exposed through the base and filter mosaic, so that a single exposure made simultaneously three separate records on the same sensitive surface. Each part of the scene would record only behind those filters of a colour appropriate to it. When the emulsion was developed by reversal processing to a positive, the image would let more or less light through the tiny filters, depending on the colour of the original object recorded at that point. When seen from a sufficient distance, the pattern of red, green and blue dots merged to form a continuous coloured image. The mosaic colour processes were the only additive methods in which a colour image was given directly without the need for viewing lenses and filters. While the method worked well enough for still photography, where a relatively large plate or film was viewed directly, the huge magnifications involved in projecting cinema film at first ruled out the method for moving pictures, since the filter pattern was obtrusive on the screen. It took 20 years, after the general introduction of such processes in still photography, for a successful movie version to be produced.

The first public demonstration of the Spicer-Dufay mosaic colour processes was given in 1931. The film used a finely ruled, regular pattern of blue lines alternating with lines of red and green squares, giving about’ one million filter elements to the square inch. The process had originated in the Dufay Diopticolore and Dioptichrome processes of 1908 and 1909 – glass plate methods for still photography.

Dufaycolor film was launched in 35mm size at the end of 1932, with an improved mosaic of red lines and green and blue squares. The trade press was impressed by the new process: ‘Never before had such exquisite beauty been brought to the screen . . . [the] range and purity of the colours [are] unsurpassed by any existing system’. One report noted, however that ‘a pure red seems so far elusive’. The film was manufactured for Spicer-Dufay by Ilford Ltd, who had devised a printing method for making positive copies from the positive originals. Dufaycolor was used at first for a number of short films, and sequences in the film Radio Parade of 1934 were shot in Dufaycolor when the process went into full production.

There were mixed reviews of the film: the Kinematograph Weekly said that the Dufaycolor sequences were ‘not up to the highest standards’.

They had been shot in the studio, unlike the earlier demonstration films, and although the studio lighting had been quadrupled, it was still inadequate. For smaller scale studio use, and out of doors, the process worked very well. (See illustrations on previous page.) The positive to positive process, however, had its drawbacks, and in due course a negative-positive process was developed, made possible by the creation of special developing and printing techniques.

The camera film was given a single development to produce a colour negative in which not only was the tone range reversed but also the colours, which were reproduced as complementary to those of the original scene. Red was reproduced as blue-green, yellow as blue, green as magenta and so on. A mosaic print film was used for the prints, restoring the original tonal range and colours. The improved process was launched by the newly formed Dufay-Chromex company in 1937, when it was used to film King George VI’s Coronation celebrations with great success, despite the poor weather.

Despite the convenience of the process, for which completely standard cameras and projectors were suitable, Dufaycolor was not widely used. Advertising, travel and documentary films were made but the only feature film was Sons of the Sea, made in 1939 and generally released in 1940. At its best, the colour could be very good, but the mosaic of colour filters, small though they were, was obtrusive on the screen, at least from the seats nearer the screen, since in a large cinema the frame was magnified in area 100,000 times or more. In addition, Dufaycolor suffered from a drawback inherent in all additive processes. The red, green and blue filters through which the pictures were projected by their very nature absorbed two thirds of the available projection light. Even in the brightest parts of the picture screen brightness was less than one third of that of a black and white film shown under the same conditions. If the colour filters were made lighter to increase the brightness of the projected pictures, then the depth of colour was correspondingly reduced.”

Although it did not always bear Dufay’s name, the process he invented in 1907 was pursued in modified forms and under various names for over forty years – covering much the same period as the Autochrome process.

Louis Dufay, son of the notary in the small town of Baume les Dames near Besançon, was born in 1874. After studying law and working in a practice in Chaumont, he somehow became interested in colour photography and then conceived, and in 1907 patented, a method for producing a geometric filter réseau for a screen-plate.

In his patent, Dufay described this procedure at some length.

Briefly, a transparent support, having been coated with a thin layer of gelatine, was covered by a pattern of parallel greasy ink lines to serve as a temporary resist. The gelatine between the ink lines was then dyed red. The surface of the plate was then coated with a varnish that adhered to and protected the dyed areas but elsewhere could be dissolved and removed together with the underlying greasy ink. Next, a new set of greasy ink lines were printed at right-angles to the first and the unprotected areas between the resist dyed blue-violet. The whole surface was again varnished and the resist removed. By now one third of the surface was coloured red and one third blue-violet in the form of alternating rectangles, while the remaining third of the area, represented by parallel lines, was dyed green to complete the mosaic.

This may seem to be a very complicated way of forming a mosaic of red, green and blue filters, and in fact the method was simplified later, when Dufaycolor was produced on film-base.

There is evidence that in 1908 Dufay tried to interest Lumière in his patent, but by then that company was probably quite happy with their method of producing a random screen pattern. He had more luck with Guilleminot, a plate and paper manufacturer with a factory at Chantilly, where Dufay and his family went to live in 1909.

A company name la Société des Plaques et Produits Dufay was formed with a capital of 420,000 Frs. and the plates were called Dioptichrome. They were on sale for only a few years, the most successful of which was 1911, when 40,000 plates were sold.

Because there were no gaps to fill between the filter elements as there were with the dyed starch grains of an Autochrome, Dufay Dioptichrome plates were faster and the results more transparent than the Lumière product. But the resolution of an Autochrome was far superior to a Dioptichrome transparency because the filter réseau of the latter only contained about 40,000 elements to the square inch compared with the millions of starch grains covering each square inch of an Autochrome.

However, things did not go smoothly and there were many difficulties and disputes, so that by 1914 the company was dissolved – possibly because the war made it impossible to continue. After the war, Dufay renewed his efforts to promote his process, this time concentrating on production of film rather than glass-based products, no doubt with cinematography in mind.

In 1920 another company was formed, this time called la Société Versicolor, with a capital of 2,900,000 Frs. By now Dufay was offering not only the attraction of a film for the cinema, but also a negative/positive paper print process based on an additive screenplate colour-negative, but requiring the prints to be made via three film-based positives obtained by making separate exposures from the colour-negative through red, green and blue filters. The three positive images were converted into subtractive primary colours (presumably by dye or chemical toning), and then superimposed to form the colour print.

A portrait studio was opened in la Place de la Madeleine in Paris. For reasons that should have been obvious, even at the time, the print process was unsuccessful and was soon abandoned. Once again there were production problems and financial difficulties so that by 1926, Versicolor must have been relieved that they managed to interest Spicers, the large paper-making company in the UK.

Spicers used the services of Thorne Baker as an expert to advise them on the potentialities of Dufay’s process and he must have reported favourably because several thousands of feet of experimental colour negative film were shot in the South of France from which prints were made and shown at the Pavilion Theatre in London in 1928.

At that time the ruling of the réseau was still very coarse – only 8 lines per mm – and image resolution would have been very poor.

Nevertheless, the results must have been good enough for Spicers, because in 1932 they invested more than £500,000 in a new company called Spicer-Dufay Limited. Soon after this, Ilford Limited joined forces with Spicers, after which another company – Spicer-Dufay (British) – was formed and by the end of 1935 Ilford was in control.

The first high-precision resist printing machine to be installed by Spicer-Dufay at Sawston in Cambridgeshire was used to produce continuous rolls of 22ins wide cellulose acetate film bearing a mosaic of red, green and blue filter elements. Later, another machine was installed that was capable of printing 42ins rolls at 10ft per minute, the resist lines being spaced 20 to the millimetre.

The sequence of printing, dyeing and bleaching operations went as follows:

1. A roll of acetate film already coated with a thin layer of blue-dyed collodion was printed with a set of parallel greasy ink lines angled at 23° to the edge of the film.

2. The printed film was then passed through a bleach bath so that the spaces between the resist lines were decolourized.

3. The film was then treated in a bath of green dye, after which the film carried a pattern of alternating blue and green lines.

4. Next, the residual ink lines were removed and a new set printed on the film, this time at right-angles to the first set.

5. The film was again treated in a bleach bath to leave a pattern of green and blue rectangles with clear lines between them.

6. The film then moved through a bath of red dye to colour the bleached areas.

Removal of the residual resist lines was followed by the application of a thin layer of protective varnish to imprison the dyes and to prevent them from reacting with the emulsion coating that followed. In fact, the emulsion was not applied at Sawston, but by Ilford Limited in their factory at Brentwood in Essex.

Even though Ilford used their fastest ‘Hypersensitive’ panchromatic emulsion to coat Dufay réseau, the speed of the film was only Weston 6, but this made it possible to use l/25th second at f8 on a bright day. The reason for the low sensitivity, common to all additive processes, was that more than 75% of the light reaching the film was absorbed by the filters. The réseau filters not only reduced the speed of the emulsion, but it also meant that very powerful light sources were necessary when it came to project an additive transparency.

Despite all these limitations, so urgent was the need to have some form of colour photography that allowed the use of ordinary cameras, that professionals and amateurs alike were prepared to tolerate the shortcomings. At that time the only alternative systems involved making separation negatives, either successively or by means of special ‘one-shot’ cameras, and then to produce a colour print on paper or film by some kind of lengthy and complicated assembly process such as trichrome-carbo or dye-transfer. In particular, the motion picture industry was looking for some alternative to the dominant Technicolor system, with its special ‘three-strip’ cameras and the necessity to have all release prints made by Technicolor’s imbibition transfer process.

King George V’s Silver Jubilee was photographed in Dufaycolor by Movietone News in 1935 and 150 copies were distributed to cinemas on the following day. At that time the only way of making copies was to use the same type of reversal film and processing as had been used for the original, but the results were not very good.

In the late 1930s Dufaycolor became popular in l6mm format for amateur cinematography, and for this application it was quite satisfactory to process the original film by reversal, and such a service was offered by Ilford.

However, it was realized that a much better way of proceeding in professional cinematography would be to process the original as a colour negative and then print it by contact to produce positives.

But there were two problems to be solved before this method of working could be successfully adopted. First, some way had to be found to avoid the moiré effects that resulted from the interaction of the two réseau patterns. Second, it was necessary to prevent the serious degradation of colour that resulted from the scattering of printing light as it passed through the two réseaux.

Some very well-known experts in the field of colour photography applied their minds to these problems and came up with solutions. Dr. D. A. Spencer devised a ‘depth’ developer that ensured the silver image remained very close to the filter réseau and therefore resulted in less scattered light when the negative was printed. Dr. G. B. Harrison, together with R. G. Horner and S. D. Threadgold of Ilford’s Research Department, devised improvements to the illumination system used in the contact printing machines and so managed to eliminate moiré patterns.

The problem was to destroy the identity of the negative réseau by the time the printing light reached the positive réseau. This was done by placing the negative and positive films front to back; separating them by the thickness of the positive base so that the printing light passed through the positive réseau before reaching the positive emulsion. By using a source of light of finite size as opposed to a point source, the projected image of the negative réseau was diffused, thus avoiding the formation of moiré patterns.

The improvement in quality that resulted from using the negative-positive system meant that a film made on Dufaycolor of George VI’s Coronation in 1937 was a considerable success and led to a number of other short films being made by Pathé, including Trooping of the Colour and Royal Naval Review.

Processing and printing facilities were established in Paris, Geneva, Rome, Johannesburg, Bombay and Barcelona, while Dufaycolor Inc. was formed to promote the process in the US. However, in 1938 Ilford Limited decided (probably with an eye on the new Kodachrome process) that the future of colour photography was more likely to lie with subtractive rather than additive systems and they sold their holdings in Dufay-Chromex Limited, a company that had been formed by Spicers Limited and Ilford Limited in 1936.

Ilford did continue to coat Dufaycolor réseau at Brentwood until after World War II, but by then it had become obvious just how much progress had been made on the development of multi-layer materials in both the US and Germany, so both technical and financial interest in additive processes quickly declined.

“The images Lye produced by hand-painting were not, of course, then copied by teams of industrious women. By 1935, when A Colour Box was picked up by the GPO, colour technology had developed to a point where duplication via one of a number of colour processes was the normal means for onward distribution. For Lye and for the publicly funded GPO Film Unit, the Technicolor process (in which Disney had a virtual monopoly, as far as animation was concerned) was a nonstarter – it was much too expensive – so the colour process chosen was Dufaycolor.

Dufaycolor was an additive red, green and blue mosaic colour process. The colours it delivered were muted and soft. All Dufaycolor was produced on safety stock (diacetate) and as a result it has its own particular problems of instability, which there is no time to discuss in detail today. Suffice it to say that much Dufaycolor material is going acetic. The NFTVA collection holds a range of Dufaycolor safety material for A Colour Box, and the BFI has produced safety Eastmancolor protection material for this title from these elements. The Eastmancolor viewing copy so produced is the copy which we have made available for screening around the world. When this Eastmancolor viewing copy is compared with our only surviving Dufaycolor positive of A Colour Box, it is clear that simply the process of transferring Dufaycolor to Eastmancolor stock increases the colour saturation somewhat. Nevertheless, we have tried to ensure that this viewing copy reflects more or less what audiences at the time would have seen in the cinemas – despite the all-too-familiar difficulties of attempting to replicate the original colour quality when using a different colour system.

At this stage it seemed that our preservation role had been completed – at least for the moment. In October 1996, however, as a result of an access request from the Len Lye Foundation in New Zealand, we re-examined our holdings and discovered a nitrate element originating from the GPO Film Unit. On examination, it transpired that this was an original hand-painted Len Lye picture element. It was accompanied by a matching nitrate sound track, and Sarah Davy, the Access officer handling the request for the Len Lye Foundation, immediately involved the Archive’s Technical Manager, Joao Oliveira. The nitrate picture element (from which the Dufaycolor pre-print material had been made in the 1930s) was by now in poor condition, and the questions facing us were these: How could we best preserve this element? Indeed, could it be printed at all?

One thing was immediately clear. The hand-painted colours on the nitrate reel were brighter and more saturated than anything the Dufay process had been able to reproduce. On further examination, Joao found that a fascinating war was going on between the different materials composing the nitrate picture element. In places the dyes or paints had interacted with the base and attacked it, making it extremely brittle and very shrunken. At other points the gases given off by the nitrate base had interacted with the dyes and discoloured them to a certain extent. The material was far from stable.

The view of the commercial labs which we consulted in the UK was that the element could not be printed. It was too fragile and too brittle. Joao was not to be defeated, however, and he undertook to print the reel, modifying one of our printers to cope with the shrinkage. An internegative was produced in the Conservation Centre’s Research Laboratory, and the colour processing was then undertaken by our colleagues at Soho Images under Joao’s supervision. With Joao supervising the grading, the new colour print was then made. The results were quite striking.

Despite the ravages of 50 years of decomposition undergone by the original nitrate, the colours on this new print are far more saturated and more intense than the Eastmancolor viewing copy produced from the Dufaycolor material. Of course, no one saw the film looking like this at the time, except perhaps when it was projected during the production process. In archival terms, it would be philosophically dangerous to argue that this is a “restoration”, or that the new copy may be closer to what Len Lye would have liked to see on the screen had he had the choice. Lye isn’t here to answer for himself, and none of us at the J Paul Getty Conservation Centre are in the habit of consulting mediums. All we can say is that we have tried to create from the surviving hand-painted nitrate a copy that replicates what survives of Lye’s original as closely as possible. We have done this in the knowledge that it is uncertain how long the nitrate may survive even in good storage, because of the cocktail of chemical reactions that are still ongoing within the element, and because the duplication process is the only one open to us to try to protect it.

In a live presentation – though sadly not in a book – it is possible to conclude by running the Eastman print made from the Dufaycolor pre-print material side by side with the Eastman positive made via the Eastmancolor internegative from Lye’s hand-painted nitrate positive, so that a viewer can see the difference in colour quality. I hope this verbal description is informative, and justifies our attempt to preserve something of the special qualities of the original hand-painted nitrate and present them on the screen.”

(Anne Fleming (2002): A Colour Box (Len Lye Recovered). In Roger Smither (ed.): This Film is Dangerous: A Celebration of Nitrate Film (Brussels: FIAF, 2002), pp. 123-127, on pp. 126-127.)

“Len Lye had previously made Tulusava (1929), where he had made 4000 drawings to give an animated effect. Lye used Dufaycolor to make Colour Box. This had initially begun as Spicer-Dufay, a mosaic colour process. The film used a finely ruled, regular pattern of blue lines alternating with lines of red and green squares, giving about one million filter elements to the square inch. The process had originated in the Dufay Dioptiocolore and Dioptichrome processes of 1908 and 1909 – glass plate methods for still photography: Dufaycolor film was launched in 35mm size at the end of 1932, with an improved mosaic of red lines and green and blue squares. The trade press was impressed by the new process, yet one trade press magazine noted that ‘a-pure red seems illusive’ (Coe).

However, when Len Lye used the process of Dufaycolour for Colour Box, on the celluloid he used paint that was transparent enough to produce bright colours-when projected. To build up colour textures on the film-strip he used a camel-hair brush, and a fine toothed comb.

Bright colour shapes — squares, dots, polygons, as well as other abstract shapes dance around on the screen to an extremely cheerful rumba.

This film is irresistible. It is like an abstract painting that makes music all on its own. It is no wonder that it was a success. Len Lye came from New Zealand. He was interested in the ‘pre-rational’. He developed his own doodling from a very early age, but also a style that was based on aboriginal art and the primitive. He made a few more films for the GPO in colour and the popular N or NW (1936) in black and white, but which also has a painterly effect experimenting with shapes and stencilling amongst other cinematographic effects such as the jump cut. After the war he went to New York and then moved back to New Zealand, and worked more on kinetic art. Colour Box can be in fact seen as a kinetic art sculpture.

If one wants to get a real sense of Dufaycolor, it is evident in two films Humphrey Jennings made in 1938 and 1939: Design for Spring, a wonderful world of soft pastels ideal for portraying the fashion show of socialite dress designer William Hartnell, who was inspired from Wedgwood blue; and Farewell Topsails about a boat, the Katie in Cornwall, which transported chalk to be used for porcelain – possibly by Wedgwood (Siambani, 90), which would in turn inspire the dress designer. These were days of peace and appeasement before the Second World War, weary and apprehensive of any violent colours.

Jennings seems to have been inspired by Dufay for his own painting. Many of his paintings of that period, but even some he made after the war insist on pastel hues, especially soft shades of blue. Jennings invented a kind of fluid cubism, which along with this Wedgwood blue formed a distinctive British style. (Siambani, 90) An improved process Dufay-Chromex was launched in 1937, when it was used to film King George VI’s Coronation with great success. However Dufay was not used extensively because the mosaic of colour filters, small though they were on the screen, could be obtrusive. (Coe, 125)

References

Coe, Brian, The History of Movie Photography, New Jersey: Eastview Editions, 1981.

“As early as 1925, the patents of Louis Dufay, a French photographer, were pooled into the Dufay-Chromex, Ltd. In America, the market was handled by the Dufaycolor Company, Inc.

During 1934, a color sequence in a film called THE RADIO PARADE was presented by Dufaycolor in England. The original appearance of the color was disappointing, but British Movietone News made some Dufaycolor news pictures of the Jubilee processions, which meant printing large number of copies successfully and rapidly. The prints suffered from a granular effect known as “boiling.” More improvements were made and a practical test was run which made a great impression on the public and the film industry alike — the test being a film of the Coronation in 1937. This was followed by several experimental films in Dufaycolor by Norman McLaren of Canada, COLOR COCKTAIL and LOVE ON THE WING.

During 1937 and 1938, a large number of Dufaycolor short subjects were made in England and on the continent. In the United States, an excellent version of a yacht race was filmed in Dufaycolor and released under the title of SAILS AND SAILORS. Other British films in Dufaycolor included TROOPING THE COLOR, ROYAL NAVAL REVIEW, ST. MORITZ, FAREWELL TOPSAILS, OLD SOLDIERS NEVER DIE and SOUVENIRS. These films proved that Dufaycolor “could equal any process in definition and accuracy of color reproduction.”108 During World War II, veteran cameraman Arthur Pereira made some experimental films in Dufaycolor. But despite its success in England, Dufaycolor could not compete with Technicolor in the United States. The process differs from the other color systems in that it is a “screen process” — that is, the back of the film is coated with a large number of minute screens in red, blue and green in such proportions that one cannot see any color in the film at all when it is held at a distance. The screens are arranged to form a regular “grid” or réseau and is developed in two stages.109 Dufaycolor unfortunately fell into disuse and while the British company continued, the company’s American branch failed in 1939.110

References

108 Cornwell-Clyne, pp. 21-22.

109 Spottiswoode, p. 208.

110 Cornwell-Clyne, pp. 21-22.”

(Limbacher (1969): Four Aspects of the Film. A History of the Development of Color, Sound, 3-D and Widescreen Films and Their Contribution to the Art of the Motion Picture. New York: Brussel & Brussel 1969, 386 pp. 44-45.)

“Dufaycolor 35-mm. film has 20 lines to the millimetre.

From Wall’s statement it should follow that the screen (réseau) would still be visible at some 60 ft., in a theatre having a 25 ft. screen, since the lines would be about 8.5 mm. wide on the screen. As a matter of fact the screen is invisible at 60 ft., and also at 30 ft. The magnification being 340 times linear, and each line being 0.025 mm. in width, the size on the screen would be 8.5 mm., which would subtend an angle of 1′ 35″ at 60 ft. (1′ 30″ is the limit of resolving power for the eye.) However, the visibility of the screen image seems to be much reduced at smaller distances by the additive effects due to movements of the position of screen elements during the projection of 24 successive pictures per second.

Dufaycolor is the only mosaic film which has so far been used with any success for cinematographic work. The process had its origin in the screen plate of Louis Dufay, which was sold from 1910 to 1917 as the Dufay “Dioptochrome” plate. B.P. 11,698, of 1908, describes the method of manufacture. A master ruled screen consisting of parallel ruled lines is used to print upon a bichromated gelatine surface coated upon glass or film. This is developed and dyed in one of the three primaries. It is then inked up like a collotype plate. The ink takes on the hardened parts of the plate and not on the coloured lines. An impression is taken upon a plain gelatine-coated plate. The latter is then varnished.

The varnish adheres to the parallel lines between the impression of the greasy lines. Upon dissolving the greasy lines [footnote 1: First suggested by Bercegol.] [8] with benzine, clear spaces are alternatively left between parallel coloured lines. The second printing is done at right angles to the first. Lastly, the third colour is applied all over the plate on a surface of saturated gelatine. Thus a screen was made by a series of imbibitions.

It is proposed to apply parallel lines of some resist, such as a greasy ink, to gelatine dyed with one of the colours, and to destroy the colour in the intervening space. A second series of lines was printed at right angles to the former and the same operation repeated. At this angle a moiré pattern would have been produced, however. In E.P. 322,433 is described the angles used in the Dufay screen to avoid moiré.

E.P. 217,557 of 1923, forms the basis of the present “Dufaycolor” process. Celluloid or like support, superficially dyed with one colour, is partially covered with resists, and the celluloid is decoloured in the unprotected parts, which are then dyed with a second colour, so that on dissolving the resists a two-colour screen results. The two-colour screen is then coloured all over with a third colour, and further resists are applied, followed by decolouring and dyeing to produce a four-colour screen. For example, a two-colour screen is first produced by dyeing one side of the film uniformly blue, and printing thereon a series of resist lines in fatty ink. A red alcoholic colouring bath is applied which destroys and replaces the blue dye-stuff in the unprotected spaces. The resist is dissolved away and a yellow alcoholic dye containing a decolouring agent is applied to the whole surface, converting the blue lines into green and the red into orange. If a four-colour screen is desired, a fresh series of resist lines is printed on the two-colour screen at any angle to the first set, and a blue-violet colouring bath containing a developing agent is applied which destroys and replaces the yellow in the unprotected parts, which then exhibit the colours blue-violet and red-violet in alternate spaces. On dissolving away the resist, a four-colour screen comprising these colours together with green and orange is obtained. Suitable dyes are Rhodamine B., Malachite-Green, Auramine, Methylene Blue, or Crystal Violet. The decolouring agents may be caustic potash or soda.”

The Dufaycolor film base is cellulose acetate (non-flam. film). [Footnote 1: Positive film base is triacetate, which is much stronger than acetate. The projection life is as long as that of nitrate film. This base is coated with blue-dyed collodion. This is done on a standard type of substratum coating machine.]

The coating is remarkably even. The collodion-coated film is then ready for the printing of the greasy resist lines. The lines are printed by an engraved steel roller, 22 in. wide (Fig. 71). The roller is engraved in France by a milling tool, the operation being comparable to the making of a calendering roller for the finishing of textiles, save that the work is much finer. The ink is a true printing oil ink, the quality of which was only determined after much experiment. It is slightly coloured blue in order to facilitate examination during the process of printing. The ink is applied by a rubber roller to the surface of the engraved roller. It is somewhat remarkable that no ink finds its way into the interstices between the raised lines. The printing is marvellously good. Very few irregularities occur. The individual line under the microscope is perhaps not absolutely even in width, but any slight unevenness is compensated by averaging. The printing machine is a beautiful piece of precision workmanship, the work it has to do is possibly the finest printing ever achieved (Fig. 72). The speed of printing is about 10 feet per minute.

The printed film proceeds direct to a festoon drier of standard type. The travel is about one hour, when it enters the bleacher and dyer (Fig. 73). (At this stage the réseau or screen is tacky.) The film first runs over a shallow tank containing a bleaching bath of alkaline-alcohol. The green dye between the resist lines is completely bleached. In continuous movement the film is then dyed green. The dye is spurted from a number of nozzles at intervals in a pipe lying across the film.

The streams fall down the réseau printed surface and form a meniscus between a roller and the film. Thus the delicate réseau does not touch any abrasive surface before the green dyeing is complete. The dyeing is practically instantaneous.

The film is then exposed to a powerful water spray to remove excess dye, after which it enters a series of benzine tanks to dissolve the last trace of printing ink. When the film leaves the machine it has upon its surface a pattern consisting of blue and green parallel lines of equal width. These lines are printed at an angle of 23° to the edge of the film.

The film is now ready for the printing of the third (red) lines, at right angles to the other lines. After the printing of the réseau is complete it is coated with a thin protective layer of special varnish. The film is then ready to be coated with panchromatic emulsion.

The present screen is printed with 20 lines to the millimetre, each line being approximately 1/40 mm. in width. Sixteen-millimetre film has a réseau of 23 lines to the millimetre. The original Dufaycolor 35-mm. ciné film is developed as a negative and prints are made by contact on Dufaycolor positive, a practically normal machine being employed, except for modifications in the light-source and light control.

By means of the “depth developer” of Dr. D. A. Spencer (see page 191), development is restricted to the lower level of the emulsion layer in immediate contact with the réseau. This eliminates desaturation due to irradiation and réseau image element spread. In the words of the inventor [12]:

Assume that a pure red object has been photographed. In the resulting negative the red elements should be masked by black silver and the green and blue elements, through which the red light from the subject cannot pass, should be transparent. Owing to the spreading of the silver image, however, these elements are partially masked by developed silver. When now we print from this negative upon similar material, to obtain the final positive, a similar unwanted scattering takes place accompanied by a further degradation of the colours.

It might at first be thought that an increase in exposure during printing would compensate for the reduction in the luminosity of the green and blue elements, which results from the density produced by light scattered from the red recording region. It must be remembered, however, that the spreading of the image is taking place from every element through which light passes and is, therefore, in effect tending to even out the amount of opaque silver produced under each element. Since the rendering of colour is dependent upon the magnitude of the difference between the silver deposits under each of the three sets of elementary colour filters, this evening out is a desaturating effect tending to destroy colour and an increase in exposure when printing will do nothing to restore the lost colour.

Furthermore, the scattering which occurs only once in the reversal processing of a camera exposure, and which is largely counteracted by the colour contrast effect, operates twice in negative-positive processing to produce an intolerable degradation of the colour rendering. Accordingly, to make negative-positive processing of combined screen material a practical proposition, the irradiation within the emulsion must be reduced to a minimum.

Since the deeper the image extends into the emulsion the greater the irradiated area becomes, any technique which will confine the image to those layers of the emulsion nearest the réseau elements should minimize the scatter responsible for the degradation.

This has in fact proved to be the case and the depth developer has been found to give results which are indistinguishable from reversal positive originals (D. A. Spencer, E.P. 470,855).

Monochromatic Printing Light.

Colour dilution may also be due to the spectral overlap in the transmissions of the colour elements of the réseau. This may be reduced to the minimum by restricting the printing light to three narrow wavelength groups corresponding as closely as possible to the maximum transmission of the three réseau colours. It is possible to print with three tungsten filament lamps used in conjunction with narrow-cut filters, the light being combined on the printing plane, but a more elegant arrangement was made possible by the advent of high-pressure mercury discharge lamps. Such a lamp is used in conjunction with a tungsten filament “Class A.1.” projector lamp of 500 watts which is filtered with a red glass of narrow-cut transmission in the red region of the spectrum. This lamp is housed behind the mercury lamp, the red light being completely diffused with a sheet of flashed opal glass. The mercury lamp has a very powerful line emission at 577 M/j, which is at an unfortunate position where the overlap in the Dufaycolor red and green filters is at its maximum. Happily a saturated solution of didymium chloride completely absorbs this line, while still transmitting the valuable emission at 546 M/f (Green) which is ideally placed. The mixed light of the mercury and tungsten after passing through a cell of didymium chloride (didymium glass is almost equally effective) consists of three monochromatic bands whose wavelengths are

670 Mμ—605 Mμ (Red) [Footnote 1: The sensitivity of the emulsion falls off rapidly at 650 Mμ so that the presence of light of longer wavelength is of little consequence.]
546 Mμ (Green)
436 Mμ (Blue)

(with certain other faint lines).

This trichromatic monochromatic light prevents each primary colour element of the film mosaic from recording light which has originated from the other two elements. The ideal is that light originating from one colour negative element, say red, should be totally excluded (or absorbed) by the green and blue positive elements. This ideal is realized in the above arrangement.

The Dufaycolor negative record consists of silver densities variously distributed over the réseau, the particular distribution determining the colour seen by transmitted light. For example, if the silver densities are distributed so that they occur only on the red elements, the negative will appear minus red (or blue-green) and will represent the photograph of a red object. The negative records the colours of the subject as complementaries, that is to say, the colours reflected by the subject are absent from the negative, all other colours being present. If the negative is now used as the subject and photographed either by means of a camera or by simple contact, the colours present in the negative will be absent from the print. The print will therefore be correctly coloured. For example, if the subject is red the negative will be minus red or blue-green, the print will be minus blue-green or red. This comparatively simple procedure is, however, complicated by the fact that the negative, unlike the subject, is divided up into a regular pattern of three colour elements, and, as is well known when two similar patterns are placed together, interference shows itself in the form of moiré which may be visible in the form of lines or squares hundreds of times larger than the dimensions of the element pattern and therefore clearly visible to the naked eye.

These moiré patterns in the special case of Dufaycolor are produced briefly as follows—the dark parts of the pattern are regions in which elements of one colour on the negative are positioned over elements of different colour on the positive so that the light has to pass through two elements of different colour, e.g. red and green. The lighter parts of the moiré pattern are produced in regions where the elements of one colour on the negative coincide exactly with elements of the same colour on the positive. Such a combination obviously transmits more light than when the coincident elements are of different colour. Prints made under such conditions will show corresponding dark and light areas.

In order to eliminate moiré patterns it is necessary to do one of two things. Either to arrange that the two réseaux, the negative and positive, coincide exactly at all points, or to destroy the identity of the negative réseau in some way such that the light falling on the positive réseau is perfectly uniform and is not divided up into small elements of different colour.

It is not possible to apply the former method of exact registration of the two réseaux because, apart from the extreme difficulty of effecting this registration with such small elements, shrinkage due to processing, etc., renders it impossible to ensure continuous registration over areas comparable with the size of a ciné picture.

It is well known that the moiré pattern produced when two réseaux are superimposed varies in size and character as the angle between the two réseaux is varied, and an angle can be found at which the pattern becomes almost invisible. The pattern is, however, still present, but is of very small size, and if printing were carried out under such conditions with no further precautions the effect on projection would be very unsatisfactory.

It must be realized that the pattern is not only undesirable because it produces a visible pattern on the screen but because the black areas which do not transmit light will fail to blacken the colour elements which should be blackened and so cause an addition of white to the colour photographed.

For example, if the colour photographed is green the negative will transmit red and blue. In the part of the print where the red of the negative falls on the blue of the positive and vice versa, the blue and red elements of the positive when finished will transmit light and the overall colour of this section will be white (since the green element of the print will transmit in any case).

It appears therefore that a suitable adjustment of the angle between the negative and positive films cannot eliminate moiré ; all it can do is to render the pattern rather less startlingly visible than it would be if the angle were such that that pattern size was several millimetres wide on the film. This fact is made use of in the actual process because it is not possible to ensure complete absence of moiré all the time owing to small variations in film shrinkage and thickness which are beyond control, so the optimum angle between the réseaux is always used so that any small residual moiré pattern has less chance of making itself apparent.

From what has been said it will be apparent that the problem is to devise a method of destroying the identity of the negative réseau by the time the light reaches the positive réseau. In other words, to arrange that the positive réseau is uniformly illuminated. Or, to put it in yet another way, to ensure that the light that passes through the negative réseau is thoroughly mixed before it strikes the positive réseau.

If the two réseaux are in perfect contact no mixing of the light can possibly take place, and it is therefore necessary to start by separating the two réseaux. This can readily be done by placing the negative and positive films front to back, or back to back, thus separating the réseaux by one or two base thicknesses as the case may be. For quite another reason bound up with the desirability of arranging that the positive film is projected with the emulsion facing the screen as for black and white so that the sound track is correctly focussed, the films are placed front to back and are thus separated by one thickness of base only (this must be the positive base so that the light passes through the positive réseau before striking the positive emulsion).

By using a source of light of finite size as opposed to a point source, the projected image of the negative réseau will be diffused, and by using an extended source of definite shape and size it is possible to diffuse the projected image of the negative réseau completely, whilst retaining the maximum possible definition.

Consider first a pinhole camera. The image produced by such a camera is a perfect projected image of the object; it has the same shape as the object and its size is simply related to the size of the object and the position of the pinhole, Fig. 75.

The Dufaycolor réseau may be regarded as composed of a number of juxtaposed squares, each containing one red, one green and one blue element, Fig. 76. The red lines are actually continuous, but we can regard them as divided up by imaginary lines as indicated in the figure ; let d be the length of the side of the square (d = 1/20th mm.—0-05 mm. for 20-line réseau). Now consider a very small area of any one of the squares—a pinhole in fact—it does not matter what colour element it falls in.

Let us denote this pinhole by A in Fig. 76; the rest o f the réseau is considered black for the moment.

In Fig. 77 a perspective sketch shows the effect of casting an image of a square illuminated aperture by means of the pinhole A. As indicated in Fig. 75, by altering the size of the source or its distance, we can make the image of the source any size we wish. Suppose we arrange that the image is a square having its sides parallel to the unit squares of the réseau and equal to d. Now consider another pinhole B (Fig. 76) in an adjacent square, situated in exactly the same position relative to its square. The distance AB will be d.

Under the same conditions the image cast by B will also be a square of side d, and the images of A and B will just touch, since AB — d. By imagining a similarly situated pinhole in every square, all providing images according to the same rule, the result will be perfectly uniform illumination on the screen.

Now we can further extend this to include another complete set of similarly situated pinholes but different from the A, B set, and exactly the same arguments apply, until finally we have extended the pinholes until they cover the whole réseau surface and we have still got perfectly uniform illumination.

It follows from the above argument that the illumination remains uniform if any part of the squares is rendered opaque, providing all squares are affected in the same way, so that if all the red elements are opaque the illumination, although changed in colour, remains uniform.

This then is the method [footnote 1: See E.P. 446,679 (page 176)] employed for destroying the identity of the negative réseau on the copy screen and it only remains to find the formula relating to the various distances and sizes. Referring to Fig. 78, the negative réseau has been drawn as a pinhole because this leads to the necessary condition. The source is square and its side is D, and the condition of uniform illumination is that the projected image of this square source on the positive réseau is equal in size to the elementary square of the negative réseau, i.e. to the reciprocal of the number of lines per mm. (other dimensions must then be in mms.). It must be remembered however that in this case, although the true thickness of the base is say t, the effective optical thickness is t/μ where μ is the refractive index of the base (its value may be taken as 1.4).

From the geometry of the figure it is obvious (similar triangles) that

D/T=μd/t

where the letters denote distances as shown in Fig. 78. The dimensions d, μ and t are more or less fixed so that ratio — is fixed, but either D or T can be varied providing the other is adjusted to compensate. In practice it is desirable to make T fairly large, say 10 cm., otherwise parallax errors are introduced at the edges of the frame which might seriously affect the efficiency of the elimination of moiré at these places.

the side of the square source would under these conditions have to be 56 cm.

It is clear from what has been said that the sides of the square source must be parallel to the square réseau units, or in other words parallel to the red lines in the negative réseau.

This accounts for the angle at which the square mask is set in the printer.

In practice the above formula may be used in designing printers, but it is always desirable to allow a little latitude in the position of the mask to allow adjustments to be made.

It can be seen from the formula that if the positive base thickness changes from 5 to 5 ½ thousandths of an inch, the correct distance of the mask will change from 10 cm. to 11 cm. The difference in moiré between two such distances can be detected, and if the very best results are to be obtained the base thickness of the individual positive material being used should be allowed for. For all ordinary purposes, however, the distance may be set for the average positive thickness.

Finally it is useful to make any final adjustments of distances by means of a test assembly. This consists of two pieces of film, one of which has been fixed out. The réseau side of the fixed-out film is cemented (seccotine) to the base of the raw stock so that the red lines of the two réseaux are almost parallel and a large moiré pattern consisting of dark bands about 2 mm.

apart is visible when the assembly is placed in front of a point source. The white emulsion layer of the raw stock acts as a perfectly diffusing translucent screen and so shows the pattern as it would be recorded on the emulsion. By placing this assembly in the gate of the printer the final adjustment of the mask position can be readily determined as the position at which the pattern is least visible (it should disappear entirely at one position). If it is required to adjust the printer for a special print, a test assembly can be made in a few minutes, using a sample of the positive stock to be used in the actual printing as the raw stock; any piece of plain réseau will do for the other piece (providing it has the same size réseau as the negative to be printed, e.g. 20-line, etc.).

Records on regular pattern multicolour screen material are printed by contact on to similar material by means of a beam of diffused light from a source at which the cross-section of the beam is adjusted, according to the distance of the source from the screen associated with the original, the size of the screen elements, and the distance apart of the original and copy screens, to produce substantially uniform illumination of the copy screen. In Fig. 6a (see Fig. 79A) , if n is the distance on either side of an element of the copy screen over which the light is to be spread and d is the separation of the original and copy screens, the angle 6 subtended by the source at any point of the original screen is given by the formula 0 = 2 tan ~n/d.

In Fig. 3, light passing through the aperture 5 in a mask and through the elements of one colour, e.g. red, in the original screen 6 falls on the copy screen 7 and is spread thereover; light passing the elements of each other colour of a three-colour screen comprising red stripes and stripes formed of alternate blue and green squares, the dimensions of the light source, is calculated to give the desired spread in each direction for the red lines, the spread of the green and blue elements being then slightly too great.

Dufaycolor ciné film is made in two types, known as Type I.N. and Type I.G. The former is for work in daylight and arc lighting, the latter is exclusively for photography by the light of incandescent filament lamps. Type I.N. has a daylight Weston rating of 2. This is equivalent to a filter factor of six as compared with, say, Kodak Super X. The exposure table above gives a rough idea of the aperture for various conditions in England in the summer.

Neither of these stocks requires a filter for their respective illuminants. Type I.G. is balanced for filament lamps of about 3000° K colour temperature. On the other hand Type I.N. Dufaycolor is balanced for sunlight, or for its equivalent, high-intensity arcs such as those manufactured by Mole-Richardson with which a colour temperature of 6400° K is obtainable. (See page 66.) For exterior work Dufaycolor technicians strongly advise the use of an exposure meter such as the Weston Ciné Exposure Meter, Model 819, with the aid of which the correct aperture may be read directly. This meter possesses the advantage of a small acceptance angle (approximately 25°) corresponding to that given by a 50 mm. ciné lens. Type I.N. emulsion has a fairly long straight-line response, but the user cannot expect a latitude equal to black-and-white emulsions. For this reason serious errors in exposure are not permissible.

An error in the direction of over-exposure is much to be preferred to under-exposure. The limited scale forbids correct rendering of light values exceeding a scale of five to one.

Needless to say the object should always be to record every part of the subject on the straight-line part of the response, but in many situations this is impossible and a compromise must be made. Certainly extreme contrasts of light should be avoided unless a special effect should be required.

I.G. stock has a somewhat longer scale than Type I.N. and it has shown itself capable of rendering the subtlest gradations of colour. Exposure in the studio is generally determined with a special Weston [footnote 1: Weston Model 594 "Photronic" cell used in conjunction with a Model 301 specially calibrated D.C. micro-ammeter.] meter reading light values directly in foot-candles. The artists should be lit at a brightness level of about 800-1000 foot-candles. Highlights should not exceed 1200 foot-candles. Backgrounds, if light, should not fall below 250 foot-candles. Thus the range in which detail will be well rendered and local colour correctly reproduced is within the five-to-one range mentioned above.”

“The most successful of all the screen processes was the one initiated by Louis Dufay. Today the product is known as Dufaycolor, but it was first introduced about 1910 as the Dioptichrome plate. The first Dufay patents were assigned to an organization carrying the quaint name “A Company for the Exploitation of the Process in Color Photography of L. Dufay.” This became the Versicolor organization. Some time later Spicers Limited became interested and such companies as Spicers-Dufay, Ltd., Dufaycolor, Ltd., and Dufay-Chromex, Ltd., were formed to exploit the disclosures. Finally the Ilford company became interested. In the United States there was but one organization, Dufaycolor, which marketed the product.

The first Dufay disclosures (Eng. P. 11698/08; Ger. P. 237755; U.S.P. 1003720) were concerning the preparation of the Dioptichrome plate, which combined dichromate printing and transfer a la wash-off-relief, for the formation of the screen. A variation of this was contained in English patent 18744/08.

In another disclosure, the cutting through of a resist was adopted, thus following du Hauron and R. de Bercegol (Fr. P. 370956, addition 7138, 388616, additions 10541, 13132, and 13775; 408552, additions 11696, 118454, 442881, addition 19753; Eng. P. 15027/12 and 27708/12; Ger. P. 273629; U.S.P. 1155900). This last group of patents was already assigned to Versicolor.

The modern Dufaycolor film is prepared in accordance with the disclosures in L. Dufay’s English patent 217557 and United States patent 1552126, also assigned to Versicolor. A celluloid film is stained superficially with a “blue” dye, and on this is printed a series of parallel lines in a greasy ink. When this is treated with an alcoholic solution of a “red” dye, the “blue” is removed and replaced by the “red.” This is accomplished instantaneously if the second solution is made alkaline. After the resist is removed, the entire film is dyed yellow. This converts the “blue” and “red” into green and orange, this indicating that the original colors were really cyan and magenta. A new series of resist lines is now printed at right angles to the first, and the places free from resist are treated with a blue-violet dye solution. This will remove the yellow dye completely, and the cyan and magenta but partially. These will become converted into a blue-violet or red-violet respectively. Dufay claims a four-color process here, but it appears a rather dubious claim, since the last two colors would have a tremendous overlap, hence are not really independent of each other. As an example, the first dyeing is made with methylene blue.

The second is made with Rhodamine B. The yellow overall is made with auramine.

At this stage the lines will be true primary red and green. After the final operation, the yellow becomes replaced with crystal violet, a dye that transmits much more blue than red, but still a significant amount of that primary.

This on top of Rhodamine B will give a reddish violet, a color that will transmit red and blue freely, but no green. This certainly cannot be considered as a unit in a four-color process, since the same colors will be registered simultaneously under the red and the blue elements. These last will be formed at those places where crystal violet overlays the methylene blue. The first will prevent any green rays from being transmitted, while the second will prevent the red rays from being transmitted. But both will transmit the pure blue.

It is interesting to note that every claim made so far by the inventors of four and more color processes, fails when analyzed in this manner. They only succeeded in destroying the purity of the color analysis.

The last patent issued to L. Dufay was the United States patent 1805361, issued in 1931, and assigned to H. Wade. The corresponding English patent 322432 was issued to H. Wade and assigned to Versicolor, a rather curious state of affairs. The American patent introduces a few names which later play a prominent part in the further development of Dufaycolor. The film base is prepared in accordance to the disclosures of H. J. Hands (Eng. P. 279139, 281803 and 294008). This is coated with a layer of collodion, dyed green by the addition of 2 cc of a stock dye solution to 30 cc of the collodion.

This is a development of C. Bonamico (Eng. P. 321222). The stock dye solution has the following composition:

Malachite green 4 parts
Auramine 6.7 parts
Alcohol 100 parts

About 25 cc of collodion is used to coat an area measuring 100 by 25 centimeters, yielding a layer that is 0.01 mm thick when wet, and from 0.0002 to 0.0005 mm when dry. On this is ruled a series of lines with a resist ink. This was done in accordance with the disclosures of H. Wade (Eng. P. 322454; U.S.P. 1760048).

Fifteen lines were drawn to the linear millimeter by means of a steel roller, at an angle of 23 degrees to the axis of the cylinder. This corresponds to 400 lines to the inch. The present material is somewhat finer, containing approximately 500 lines to the inch, and some screens were made in this manner with 750 lines to the linear inch. The ruled lines were dried for one hour, and then bathed in a solution whose composition was as follows:

Alcohol 100 parts
Aqueous KOH, 10% 2 parts
Acetone 4 parts

Treatment in this solution removed the dye from the clear spaces, which are re-dyed by passing over a dye roller. The film base was thoroughly washed to remove excess dye, then it was passed through a solvent which removed the resist lines. A buffing action prepared the surface for a new set of lines, ruled at right angles to the old. The spaces clear of ink lines were again decolorized by the action of the alkaline-acetone-alcohol solution, and the un-dyed portions dyed blue by means of the following bath:

The film base was cleared as before, then coated with a panchromatic emulsion.

The further development of the Dufaycolor material was carried on by J. N. Goldsmith, T. T. Baker, and C. Bonamico.

Although Dufay no longer contributed to the solution, the procedure was not changed. Rather, all efforts were centered upon the improvement of details.

The first serious problem was that of putting a superficial coating of dye upon the film base, before the resists were applied. This coating must be absolutely uniform, and of sufficient density to act as a complete filter for one primary. The thickness of the coating must be kept to a minimum, otherwise the slight divergence of the rays after passing through the screen will cause the deposition of densities of one color under the areas intended for the other two. It is the screen which is in the rear focal plane of the lens system, so that divergence of the rays starts in the plane of the screen. Acid dyes do not stain collodion, so that the screen colors are limited to the basic dyes. But celluloid, which is collodion to which camphor and other plasticizers have been added, will not stain when treated with basic dyes. It seems that the addition of the plasticizer extensively changes the properties of the collodion.

A whole series of patents, all issued jointly to the trio J. N. Goldsmith, T. T.

Baker, and C. Bonamico, deal with the treatment of celluloid film to make it receptive of basic dyes. It is to be recalled that the basic patent (Eng. P.

322432) utilized a film base of cellulose acetate, and that this was coated with a layer of collodion dyed green. The first disclosure in which the attempt is made to prepare the film base itself for a superficial dyeing, is in English patent 333865. The base is treated with an alcoholic potash solution, ranging from one-half to five per cent of the dye. After this treatment, it will take on dye uniformly from a bath such as

A coating such as this readily takes up basic dyes from solutions that would have no effect whatsoever upon celluloid. Therefore the coated film base could receive its superficial dyeing on one side with the absolute assurance that the other side would remain clear. This represents a tremendous simplification in the manipulations of the film base during the period of the screen formation. In a later patent there is disclosed still another scheme for putting a superficial coating of cellulose acetate on the film base (Eng. P. 337073).

The film passed around a roller which just dips into a solution of cellulose acetate in acetone, such as

Cellulose acetate 14-15 parts
Plasticizer 5-6 parts
Acetone 100 parts

The above treatment yields a layer which has a thickness of 4 to 8 μ (0.004 to 0.008 mm). Such a coating will not absorb the dye, but it can be given a surface coating of collodion which is already dyed. The cellulose acetate evidently acts as a subbing base for the dyed collodion layer.

The various difficulties encountered in the making of a uniformly dyed surface layer are discussed in English patent 339238. It is very difficult to apply a dye to a celluloid film, but once applied, the dye is retained with great tenacity.

This makes its subsequent bleaching extremely hard. This can be overcome by the application of a coating of pure cellulose acetate to the surface, as is disclosed in English patent 334265. When a film base of cellulose acetate is to be used, other difficulties arise. Too deep a stain is taken up, and one which does not discharge easily. Coating such a film layer with collodion (Eng. P. 322432) helped alleviate this situation. In either case, however, the precautionary measures were nullified if the dye diffused beyond the superficial layer into the film base itself. To prevent this, the film may be dyed from a solution which is non-penetrating. This is accomplished by dispersing or dissolving the dye in castor oil, castor-oil-alcohol, or gum arabic mixtures.

To insure that the sound-track areas of motion picture film would be left free of screen pattern, C. Bonamico (U.S.P. 2008239; Eng. P. 356816 and 414761), and T. T. Baker (Eng. P. 335899) so constructed the rollers which printed the resists that no deposits were made in those areas which, after slitting, would correspond to the sound-track region.

The next problem to be tackled was that of coating. Here it was necessary to insure the firm adhesion of a gelatin layer to another of rather complex structure, and one which contained basic dyes. These were not always neutral with regard to their action upon the photographic emulsion. Some of the dyes may act as sensitizers, while others may have the opposite action and act as desensitizers. So the simplest procedure to adopt was to insulate the screen layer from the emulsion. This was disclosed by T. T. Baker (Eng. P. 401719; U.S.P. 1962679) and by H. D. Murray, H. Baines, and R. A. S. Grist (Eng. P. 435484). A solution of resin in benzol to which some linseed oil had been added, was the Baker solution.

A complete specification for the formation of the screen is disclosed by T. T. Baker (Eng. P. 420824; U.S.P. 2030163). The reason for this patent is to protect the printing of the resist lines by means of a special roller, where nonprinting areas contain an ink-resisting mercury-silver amalgam. The film base is prepared in the manner disclosed by H. J. Hands (Eng. P. 243032, 281803, 287635, and 301439). On this is coated a thin layer of collodion which is dyed green by the addition of 2 cc of a stock dye to 30 cc of collodion. The dye is prepared by dissolving 4 parts of malachite green and 6.7 parts of auramine in 100 parts of methyl alcohol. A strip 100 by 26 centimeters requires from 22 to 25 cc of the dyed collodion solution. This had been disclosed previously by C. Bonamico and H. Wade (Eng. P. 321222). Upon the dyed film is then printed a series of resist areas, which may or may not be in the form of a geometric pattern, by means of a special roller.

This is prepared in the following manner. A metal roller is first given a coating of silver. Upon this is deposited an even coating of chromium, also electrolytically. On top of the chromium is placed a sensitized tissue upon which the screen pattern has been photographically printed. The tissue used is a dichromated gelatin or other colloid. It is placed with the image portion adjacent to the surface of the roller. Treatment with hot water removes the non-image portions, leaving a tanned colloid relief image upon the surface of the roller. This is next subjected to the action of a solution which will etch the chromium wherever this surface has been laid bare, obviously between the tanned colloid relief areas. When the chromium surface has been etched away, leaving bare the silver, the etch is stopped. The tanned colloid resist is removed, and the roller treated with a mercury solution. Only the silver will form an amalgam, the chromium being insoluble in mercury. An amalgam surface has the extremely useful property of acting as a resist to greasy inks, while the chromium surface will adsorb the ink. Thus a matrix is formed by means of which a resist containing a superficial coating of dyed collodion can be transferred to the cellulose acetate film. This technique is a well established one in the photomechanical printing industry, especially in that section which uses planographic printing with mercury inks.

After the resist has been transferred, the dye in the areas between the lines is bleached by treatment with

The bleached areas are then re-dyed by treatment with an 8 per cent alcoholic solution of basic red N. The old resist lines are removed by treatment with a suitable solvent, and a new set of lines printed at right angles to the first.

Decoloration is again accomplished in the areas between the greasy lines, this time both red and green being removed. At this stage the film base consists of a series of squares of red and green lying in juxtaposition, and running in lines.

The lines are separated from each other by clear undyed lines that are free from grease, and which can therefore be stained from alcoholic solutions. This is accomplished by means of a blue bath, whose composition is the same as the one given above (cf. p. 168). A wash removes excess dye, while treatment with a solvent removes the greasy lines. The screen elements are then coated with an insulating layer of varnish, which also serves as a subbing for the panchromatic emulsion which is coated upon the varnish layer. There are several schemes which cannot readily be classified in any group.

F. J. H. Harrison (U.S.P. 578147) used a band of celluloid that was colored solidly, and ruled with opaque lines which were twice the width of the transparent spaces between. The celluloid “ribbon” was divided into three sections, each of which was stained in a different primary color. The lines in each section were staggered with respect to those in adjacent sections. The ribbon was moved by means of a spring motor across the front of the sensitive plate. The result was the same as if the plate were exposed behind a screen composed of colored lines lying in juxtaposition. It is hard to determine just exactly what advantage there was in this procedure outside of the fact that it is quite simple to prepare such a screened ribbon, for the subsequent separation or the preparation of a colored transparency would impose a very ticklish problem of registry. Similar ideas were expounded by C. L. A. Brasseur and S. P. Sampolo (Eng. P. 8390/96) ; and by F. E. Ives (U.S.P. 648748 and 666424).

In the Ives procedure, the black-and-white screen was placed in front of the plate, and the three exposures were made through the three niters. Between the exposures, the position of the screen was shifted, so that a new area was exposed on the film each time, and through a different filter.

A rather simple procedure was adopted by M. Obergassner (Ger. P. 263819; Fr. P. 438746). A plate was coated with dyed gelatin. It was then grooved through to the glass in a series of parallel lines. After recoating with another layer of dyed gelatin, a new set of grooves was cut through. The plate was recoated a second time, buffed even, then coated with a panchromatic emulsion.

It is to be recalled that the earliest patents of du Hauron and Bercegol utilized a technique identical to this, except that they cut grooves through a resist surface. This, therefore, is a simplification of the earlier disclosure. C. L. A. Brasseur (Eng. P. 20909/08; Ger. P. 219977; U.S.P. 976118) combined photomechanical printing methods with the dusting-on procedure. He printed a tacky material upon a glass or film base, then dusted on colored powders.

This was followed by another printing and dusting, until the film surface was completely covered. F. Faulstich also combined two methods (Eng. P. 152002). A base was sprayed with a dye so that only part of the total surface was covered. The covered areas then acted as resists for a further dyeing operation. Somewhat similar in basic principle was the technique adopted by Keller (Eng. P. 244644). He sprayed a gelatin-coated base with colors compounded to contain alum or formaldehyde. These chemicals tanned the gelatin in situ with the dye powder, making that specific area no longer receptive of dyes, if these were of the pinatype group.”

“Dufaycolor, manufactured by Dufay Limited (formerly Dufay-Chromex Limited), is the single remaining prominent additive three-color process available in recent years. It is of the “combined” screen-plate type, having a “regular” mosaic consisting of blue and green squares with red lines. There are approximately 1,000,000 color filter elements per square inch of screen surface.

To obtain the screen, or “réseau,” the base is first coated with a thin layer of collodion dyed blue. Greasy ink lines are printed on the surface of the collodion. These protect the underlying areas while the rest of the collodion is first bleached, and then dyed green. The greasy ink lines are removed, and a new set applied at right angles to the first set. The blue and green collodion, except for that protected by the lines, is again bleached and, this time, dyed red. Removal of the greasy inked lines gives the completed screen. The réseau is then coated with a thin protective layer of varnish, followed by the panchromatic emulsion. A diagram of the cross section of the completed film is given in Fig. 8.14. Exposure of the emulsion is through the support, and development is ordinarily by reversal. To obtain large numbers of duplicate prints, a negative-positive technique is sometimes used.

Dufaycolor is sold in roll film, film packs, and for motion pictures.

It is commonly used as a camera film and, when developed, used for direct viewing as a transparency, or is projected (Dufay-Chromex, 1949; Spencer, 1948).”

Dufaycolor was based upon a four-colour screen still photography process invented by the Frenchman Louis Dufay in 1908 called the Diopticolore process (which went on the market in 1909 as Dioptichrome). The colour photographic image consisted of pairs of lines of complementary colours, such as magenta and green, placed at right angles to a series of non-complementary colours, such as cyan and yellow. This produced a mosaic pattern of green lines interspersed with rows of red and green squares. By 1912 the mosaic had been changed to consist of blue lines alternating with rows of red and green elements shaped like capsules, and by 1917 the name of the process had been changed to Dufay Versicolor. A company, also called Versicolor, was formed to exploit it and to develop it for cine film but in 1920 it ran into financial difficulties and T. Thorne Baker, a colour expert from Britain working for Versicolor, was asked by the British paper manufacturing firm Spicers to report back to them on the possibilities of the process. In 1926 Spicers bought the process, and set up Spicer-Dufay the same year.

Spicers successfully adapted the process for cine film between 1926 and 1931 under Thorne Baker’s direction at the Spicer plant in Sawston, Cambridgeshire. They altered Dufay’s original process with a new mosaic pattern, called the réseau, made up of red and green lines overlaid at right angles. The réseau was printed onto the back of the film stock. In the camera the film was loaded with the base facing the lens and the light passed through the réseau, through the base and onto the emulsion. In projection the light had to shine first through the emulsion, then the base, then the réseau meaning that in projection the print had to be laced with the emulsion facing away from the screen, the opposite of normal projection. The research was presented as Dufaycolor in 1931, first at the Royal Society in March, and then at the British Kinematograph Society (BKS) in September.

Despite being well received, Dufaycolor had significant problems. First, although the angles of the lines of the réseau had been chosen to minimise its visibility on projection, by Spicer-Dufay’s own admission, the lines were visible as a series of diamond shapes on the image from the first six rows of any cinema. Second, the process as displayed to the BKS was a 16mm reversal process, which was more in keeping with home movies than commercial production, which relied upon a negative to positive printing process. Third, as the film had to be laced a different way from normal in both the camera and the projector, when using Dufaycolor both projectors and cameras required recalibrating. In addition, because the image on the emulsion was projected through the base, the image was darker than normal film and, on films with a combined soundtrack, the sound was quieter, meaning more light was required in projection.

Having raised their profile with the presentations in 1931, Spicer-Dufay continued research and a 35mm reversal film was launched at the end of 1932. The same year the British photographic firm Ilford invested in the company and the process and Spicer-Dufay (British) Ltd was registered in February 1933 with a capital of £600,000. Ilford’s main objective was the development of a 16mm colour cine film for the amateur market, and this was the direction taken by the company throughout that year and most of the next. The new 16mm colour film, along with an improved 35mm stock, was presented at the Savoy Hotel in April 1934, and the 16mm film was released onto the market in September to great success.

Having broken into the amateur market and fulfilled the aims of Ilford, Spicer-Dufay turned its attention to the problems which prevented a breakthrough in professional production, notably the cost of using the process, problems with shooting in artificial light and the fact that Dufaycolor was a reversal process and unsuitable for negative to positive printing. Dufaycolor prints cost around 3.5 pence per foot to make, about three and a half times that of black-and-white prints. For a film with a length of 1,000ft, this expense was considerable but not disastrous, but for feature-length films of 6,000ft or more, the extra few pence a foot added a substantial amount to the budget. In addition, although Dufaycolor was simple to use out of doors, requiring only a gelatine filter and some minor adjustments in the camera, its use in artificial light was problematic. It required at least one and a half times the usual amount of light for interior lighting, and also required that light sources were not mixed – for example, arc lamps and tungsten lamps – in order to maintain neutral balance in the colours.

The added complications of interior shooting, plus the extra cost involved, served to limit the attractiveness of Dufaycolor for the feature market, but did not prohibit its use in shorter subjects. In 1935 Spicer-Dufay (British) Ltd struck a deal with British Movietone News to film the Silver Jubilee of King George V. That same year Len Lye completed his abstract film The Colour Box in Dufaycolor, and it was acquired by John Grierson for the GPO Film Unit as an advert for the sixpenny parcel post. Although in December the British feature film Radio Parade of 1935 was released, featuring two sequences in Dufaycolor, and raised the profile of the process, it did not mark the start of a profitable relationship between Dufaycolor and the feature film sector.

In January 1936 Spicer-Dufay became Dufay-Chromex, having merged with Chromex, a holding company formed to take over British Cinecolor, and in October 1936 the company finally solved the problem of reversal printing and announced the perfection of a negative to positive printing process, which went into full-scale production in April 1937. The arrival, also in 1937, of Adrian Klein, who had previously worked for Gasparcolor, signalled the start of Dufaycolor’s most productive phase. Keen to promote the process for commercial use, Klein instigated a series of short films to be produced in-house. Humphrey Jennings was hired as director since he had previously worked in Gasparcolor on the Shell advertising film The Birth of the Robot (1936). At the same time, Dufay-Chromex perfected a reduction process whereby 16mm Dufaycolor prints could be made from 35mm negatives, an ideal situation for the shorts market, which was predominantly distributed on 16mm. Following on from Klein’s successful experiments with Jennings, independent commercial companies including Rayant Wanderfilms, Inspiration Films, Publicity Films and Merton Park adopted the Dufaycolor process, with 1938 and 1939 seeing the release of over fifty short films in Dufaycolor. Finally, in 1939, a complete feature was made in the process, Sons of the Sea directed by Maurice Elvey. A second film was announced, but stalled with the start off World War II. Dufay handed its labs over to war work, expanding on their work with filters to become one of the world’s largest suppliers of plastic glass substitutes, and by the time the war ended, Technicolor and subtractive colour was dominant. In response, Dufay-Chromex began to develop its own subtractive process, Dufaychrome.

Brown, Simon, ‘Dufaycolor: The Spectacle of Reality and British National Cinema’, www.bftv.ac.uk/projects/dufaycolor.htm [Note: This entry has been adapted from material previously published in this article.]